It is often desired to take a biological sample contained in an individual sample holder and to transfer it to one or more well plates or other objects appropriate for carrying out reactions with it (e.g., onto test strips). A single biological sample (e.g., human blood) may be divided up among a number of these downstream containers in order to be subjected to a wide variety of different tests.
Among the desiderata for the handling of biological samples are: (a) Ability to obtain a number of measurements from single blood draw. (b) Generating no waste in the sample transfer. (c) Providing a proportionate amount of fluid, particulates and cells with a transfer and overcoming challenges in achieving this at small volumes. (d) Enabling newer diagnostics that can use small samples to have consistent sample delivery. (e) Elimination of manual pipetting and associated wastes and interaction with tips, sharps, capillaries, and needles, so improving lab safety. (f) Reducing the training required for lab technicians to achieve high-quality small volume sample transfer.
Acoustic ejection is a known way of performing transfers of biological samples. In acoustic ejection, a piezoelectric transducer driven by a waveform chosen by a controller generates acoustic energy. The energy is focused by means of an acoustic lens and coupled to a reservoir containing fluid through an acoustic coupling medium, typically water. If the focused energy has a focal point inside a fluid in the reservoir and close to a free surface of that fluid, a droplet may be ejected. Droplet size and velocity may be controlled via the chosen waveform.
Current acoustic instruments rely on an active control of both the transducer and reservoir position. Typically, this involves sending a motion command to a motion controller which then initiates movement of an acoustic ejector on one or more axes. Motion in the horizontal plane aligns the transducer with the selected reservoir and motion in the vertical audits the reservoir and focuses the acoustic ejector for droplet transfer. In some contexts it is desirable to accomplish acoustic ejection by a simpler and smaller system that does not require complete control of the location of both the transducer and the reservoir.